1. Field of the Disclosure
The present disclosure relates generally to image forming devices and more particularly to a partial internal shunt and partial external shunt assembly for a magnetic roll of a dual component development electrophotographic image forming device.
2. Description of the Related Art
Dual component development electrophotographic image forming devices include one or more reservoirs that store a mixture of toner and magnetic carrier beads. Toner is electrostatically attracted to the carrier beads as a result of triboelectric interaction between the toner and the carrier beads. A magnetic roll includes a stationary core having one or more permanent magnets and a sleeve that rotates around the core. The magnetic roll attracts the carrier beads in the reservoir having toner thereon to the outer surface of the sleeve through the use of magnetic fields from the core. A photoconductive drum in close proximity to the sleeve of the magnetic roll is charged by a charge roll to a predetermined voltage and a laser selectively discharges areas on the surface of the photoconductive drum to form a latent image on the surface of the photoconductive drum. The sleeve is electrically biased to facilitate the transfer of toner from the mix of toner and carrier beads on the outer surface of the sleeve to the discharged areas on the surface of the photoconductive drum forming a toner image on the surface of the photoconductive drum. The photoconductive drum then transfers the toner image, directly or indirectly, to a media sheet forming a printed image on the media sheet.
In general, the sleeve of the magnetic roll has a greater axial length than the core such that axial end portions of the sleeve extend past both axial ends of the core. The magnetic field lines from the core extend past the axial ends of the core and attract fine amounts of carrier beads and toner to the surface of the sleeve past the axial ends of the core. Toner from the surface of the sleeve past the axial ends of the core is generally not dense enough to form full quality images on the surface of the photoconductive drum. Accordingly, transfer of toner from the surface of the sleeve past the axial ends of the core to the surface of the photoconductive drum at the outer axial portions of the photoconductive drum is undesired.
The presence of unwanted carrier beads and toner on the surface of the sleeve past the axial ends of the core also increases the risk of leakage of carrier beads and toner from the system. During operation, carrier beads and toner may tend to accumulate on the outer axial end portions of the sleeve and leak past the axial ends of the sleeve potentially contaminating other parts of the system. Carrier beads and toner may also leak past the axial ends of the sleeve if a unit containing the reservoir and the magnetic roll is accidentally dropped during shipment of the unit.
One method to reduce the unwanted transfer of toner from the surface of the sleeve past the axial ends of the core to the surface of the photoconductive drum includes extending the length of the photoconductive drum and the charge roll in order to charge the surface of the photoconductive drum at the outer axial ends of the photoconductive drum to a voltage that will resist the charged toner. However, increasing the length of the photoconductive drum and the charge roll increases the cost and size of the system and does not address the leakage risk.
Another method to reduce the unwanted transfer of toner from the surface of the sleeve past the axial ends of the core to the surface of the photoconductive drum includes placing a magnetic shunt in the shape of a circular washer on a shaft of the magnetic roll and against each axial end of the core inside of the sleeve. This type of magnetic shunt is referred to as an internal shunt because it is positioned inside of the sleeve. Each internal magnetic shunt extends to the outer radial edge of the core around the entire circumference of the core. Each internal magnetic shunt is composed of a magnetically permeable metal that redirects the magnetic field lines from the axial ends of the core back into the core to decrease the distance that the magnetic field lines extend axially past the core. As a result, the internal magnetic shunts reduce the amount of carrier beads and toner on the surface of the sleeve past the axial ends of the core. However, these internal magnetic shunts do not address the leakage risk.
Accordingly, an improved method to reduce the amount of carrier beads and toner on the surface of the sleeve of a magnetic roll past the axial ends of the core of the magnetic roll and to reduce carrier bead and toner leakage is desired.